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| United States Patent |
5,037,875
|
|
deGaravilla
|
August 6, 1991
|
Antistatic polymer blend
Abstract
The dissipation of static electricity from film of ethylene/carboxylic acid
copolymer is improved by the incorporation of a combination of antistatic
compounds therein, viz sorbitan monooleate and certain alkyl phenol
poly(ethylene oxides).
| Inventors:
|
deGaravilla; James R. (Silsbee, TX)
|
| Assignee:
|
E. I. du Pont de Nemours and Company (Wilmington, DE)
|
| Appl. No.:
|
636921 |
| Filed:
|
January 2, 1991 |
| Current U.S. Class: |
524/317; 524/339; 524/910 |
| Intern'l Class: |
C08K 005/36 |
| Field of Search: |
524/317,339,910
|
References Cited
U.S. Patent Documents
| 4053540 | Oct., 1977 | Argurio et al. | 524/317.
|
| 4379197 | Apr., 1983 | Cipriani et al. | 524/317.
|
| 4425268 | Jan., 1984 | Cooper | 524/317.
|
| 4578414 | Mar., 1986 | Sawyer et al. | 524/317.
|
Primary Examiner: Michl; Paul R.
Assistant Examiner: Yoon; Tae H.
Claims
What is claimed is:
1. A blend capable of being melt fabricated into an antistatic film
comprising copolymer of ethylene with an alpha, beta-ethylenically
unsaturated carboxylic acid having from 3 to 8 carbon atoms, said
copolymer having 0 to 90% of the carboxylic acid groups neutralized by
metal ions, and an antistatic effective amount of the combination of the
compounds sorbitan monooleate and alkyl phenol poly(ethylene oxide)
wherein the alkyl group contains from 8 to 10 carbon atoms and the number
of ethylene oxide units is from 0 to 16.
2. The blend of claim 1 wherein the total amount of the antistatic
compounds is about 0.75 to 2.5% based on the weight of the copolymer plus
the compounds.
3. The blend of claim 2 wherein the weight ratio of said monooleate to said
alkyl phenol is about 3:1 to 1:3 parts by weight.
4. The blend of claim 1 wherein said copolymer is ionomer.
5. The blend of claim 1 melt fabricated into the form of a film.
6. The film of claim 5 wherein said film is unsupported.
7. The film of claim 5 wherein said film is supported.
8. The film of claim 5 having a static decay from 5000 volts to 500 volts
in less than three seconds at about 12 days after film manufacture and
storage at 70.degree. C. and 50% relative humidity in air.
9. The film of claim 5 wherein the static decay occurs in less than two
seconds at about 14 days after said manufacture and storage.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of a particular combination of antistatic
compounds to produce synergism in the dissipation of static electricity
from a polymer host for the compounds.
2. Description of Related Art
Polymer films in the course of their handling during manufacture can
develop high charges of static electricity which can have harmful
consequences ranging from sparking, possibly causing fires, to adhering to
oppositely charged surfaces to interfere with use of the film in packaging
operations. For example, film used to package food may be more
advantageously handled in the packaging operation if the film is not
attracted to the food. Film attraction for the food can prevent the
desired wrinkle-free packaging of the food by the film.
A wide variety of antistatic compounds are available for incorporation into
polymer films for reducing static electricity charges of the film, with
varying efficacy depending on the polymer and the antistatic compound and
the amount of compound that can be tolerated by the film before suffering
loss of other desired properties. A publication of ICI Specialty Chemicals
entitled "ATMER.RTM. Antistatic Agent for Thermoplastic Polymer
Applications" (11/87) discloses a large number of antistatic compounds.
In the case of film of ethylene/carboxylic acid copolymer which may be
partially neutralized to form ionomer, improvement in its antistatic
performance is desired. Heretofore, there has not been a commercially
viable antistatic additive for incorporation into this acid polymer in
film form.
SUMMARY OF THE INVENTION
The present invention involves the discovery that the incorporation of a
certain combination of antistatic compounds in film of the acid copolymer
provides improved dissipation of static electricity.
More particularly, the present invention is a blend capable of being melt
fabricated into an antistatic film comprising copolymer of ethylene with
an alpha, beta-ethylenically unsaturated carboxylic acid having from 3 to
8 carbon atoms, said copolymer having 0 to 90% of the carboxylic acid
groups neutralized by metal ions, and an antistatic effective amount of
the combination of the compounds sorbitan monooleate and alkyl phenol
poly(ethylene oxide) wherein the alkyl group contains from 8 to 10 carbon
atoms and the number of ethylene oxide units is from 0 to 16.
Film which is melt fabricated from this blend has superior antistatic
properties as compared to film made using either of the antistatic
compounds by itself in the copolymer in an amount equal to the total
amount of the combination of compounds used in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The copolymer used in the present invention is either the acid copolymer or
the ionomer obtained therefrom. Description of the preparation of these
copolymers and the melt fabrication of film therefrom is provided in U.S.
Pat. Nos. 4,248,990, 3,264,272, and 4,351,931. The copolymer can be random
or non-random, but random is preferred. Preferred unsaturated acids
contain 3 to 8 carbon atoms and include acrylic acid, methacrylic acid,
and itaconic acid. Preferably the copolymer contains 5 to 50% of the acid
co-monomer based on the weight of the copolymer, and more preferably from
5 to 20 weight percent. The melt index of the copolymer is preferably less
than 30 g/10 min. and more preferably less than 20 g/10 min.
In the case of ionomer obtained from these acid copolymers, the preferred
metal ions for neutralizing the acid groups are Na.sup.+, K.sup.+,
Li.sup.+, Mg.sup.+2, Ca.sup.+2 and Zn.sup.+2. The preferred neutralization
is about 10 to 90%, more preferably 15 to 50% of the acid groups present
in the copolymer.
The antistatic compounds used in combination in the present invention are
available from ICI as ATMER 105 in the case of the sorbitan monooleate. A
more specific monooleate useful in the present invention is sorbitan
mono-9-octadecenoate. In the case of the alkyl phenol compound, this is
available from ICI as ATMER 508 and from Rohm & Haas as Triton N-101.
Examples of alkyl phenol compounds include nonyl phenol substituted with
an ethylene oxide adduct containing 0 to 11 ethylene oxide units, decyl
phenol substituted with an ethylene oxide adduct containing 2 to 7
ethylene oxide units and mixture thereof. Another example is octyl phenol
with an ethylene oxide adduct containing 1 to 16 ethylene oxide units.
Preferably, the alkyl and poly(ethylene oxide) adduct are para-substituted
on the phenol moiety.
The antistatic compounds are uniformly incorporated into the copolymer by
conventional melt blending techniques, e.g., the compounds are blended
with molten copolymer in a manner to form a homogeneous blend, using for
example an extruder. The compounds can be fed to the extruder along with
the copolymer feed or can be metered into the copolymer as it advances as
a melt along the extruder barrel. The resultant blend can be extruded and
cut into molding granules for subsequent melt fabrication into antistatic
film or can be directly fabricated into the film. Alternatively, the
antistatic compounds can be melt blended with the copolymer to form a
concentrate of the antistatic compounds for subsequent blending with the
copolymer used in the present invention. In the concentrate approach, the
polymer of the concentrate may be the same as the copolymer used in the
subsequent blend or can be a different polymer which, however, is miscible
with the copolymer upon melt blending.
The total amount of antistatic compounds present in the ultimate blend used
for making the antistatic film is about 0.75 to 2.5% based on the weight
of the copolymer plus the weight of the compounds, and preferably about
1.0 to 2.0 % by weight.
Surprisingly, when both these antistatic compounds are present, the
antistatic result is better than when these antistatic compounds are used
by themselves in the same amount as the total amount of the combination of
the compounds. The combination of antistatic compounds used in accordance
with the present invention gives better antistatic results than other
antistatic compounds used in the same total amount as well. It is desired
to minimize the amount of antistatic compound used for reasons of economy
and to avoid any deleterious effect on the film product, so the
possibility of adding increased amounts of antistatic compounds on an
individual basis to the copolymer is not a viable alternative.
Preferably, the proportion of antistatic compound to the combination
thereof will range from (i) 1 part of one of the compounds to 3 parts of
the other compound to (ii) 3 parts of the first mentioned compound to 1
part of the other compound, all parts being by weight. More preferably,
the combination of antistatic compounds will be 40 to 60 weight percent of
one compound and 60 to 40 weight percent of the other, to total 100% of
the combination. For both convenience and effectiveness, the combination
can consist of about equal weight proportions of each compound.
The blends of the present invention can be melt fabricated into film by
conventional methods. The film can be unsupported or it can be supported
as in the case forming a coating on a substrate. In the case of supported
film, this can be made by such conventional methods such as extrusion
coating and co-extrusion. The resultant film, whether supported or
unsupported will generally have a thickness of about 0.2 to 2 mils (0.005
to 0.05 mm). Examples of substrates for supporting the film of the present
invention include paper, foil, and other polyolefins.
The film is especially useful for wrapping articles which themselves
present a static charge that would otherwise attract an oppositely static
charged wrapping film, but is generally useful for wrapping articles. One
particularly annoying problem solved by the film of the present invention
is that the film will not attract oppositely charged food particles to the
seal area of the film package.
The improved antistatic performance of film of the present invention is
manifested by the rate at which the static charge in the film dissipates.
In the Examples, this performance is tested by the static decay test
wherein film samples are stored under controlled temperature and humidity
conditions in an air atmosphere, and these samples are removed
periodically for test. The test consists of imposing a high static charge
on the film (in air at room temperature) and measuring the time required
for the static charge to fall to a given lower level.
The dissipation of the static charge by the film is believed to involve a
surface phenomenon, wherein the antistatic compound(s) over a period of
time after film manufacture exude to the film surface to cause dissipation
of the static charge. This phenomenon takes time, in the sense that
freshly made film takes longer to dissipate the static charge than aged
film. The improved static dissipation performance of film of the present
invention takes the form of this dissipation occurring faster within the
early period after film manufacture. For example, film of the present
invention stored in air at 70.degree. C. and 50% relative humidity,
preferably dissipates a static charge of 5000 volts to just 500 volts in
less than 3 seconds at about 12 days after film manufacture, and less than
2 seconds at about 20 days after film manufacture. Preferably, this static
decay occurs in less than 2 seconds at about 14 days and even more
preferably in less than 1 second at about 14 days after film manufacture.
Examples of the present invention, in which parts and percents are by
weight unless otherwise indicated, are presented hereinafter.
EXAMPLES
In these Examples, the antistat compositions are prepared unless otherwise
indicated by blending the antistatic compound(s) with ethylene/methacrylic
acid copolymer (9 weight percent methacrylic acid, M.I.=2-3 g/10 min.) in
a Banbury mill. The mill is operated at 150.degree. C. to thoroughly melt
the copolymer and then the antistat is fed slowly into the copolymer melt,
and the operation of the Banbury is continued for about 10 min. to get
uniform incorporation of the antistatic compound into the copolymer. The
resultant blend is pelletized and the pellets are dried under a nitrogen
atmosphere overnight. The amount of the antistatic compound(s) present in
the blend is 10% by weight, whereby the blend is used as a concentrate for
incorporation into additional copolymer for fabrication into film.
Film is made by adding the concentrate pellets to the copolymer desired in
an extruder in an amount to produce the proportions of antistatic compound
desired in the copolymer, and the extruder extrudes a film tubing in which
the film thickness is about 2 mil (0.05 mm). Film samples for testing in
the static decay test are cut from this film. The film samples are
conditioned and stored at 70.degree. C. (plus or minus 2.degree. C.) and
50% relative humidity for at least 48 hours before static decay testing,
but this conditioning and storage is continuous for the life of the film
aging period during which time, film samples are removed from storage for
static charging to 5000 volts d.c. and the testing of static decay.
The antistatic compounds tested were as follows:
______________________________________
Code Antistat Compound
______________________________________
A. Sorbitan monooleate (ATMER .RTM. 105)
B. Nonyl phenol-p-poly(ethylene oxide).sub.0-11 con-
taining a minor proportion of decyl-phenol-p
(polyethylene oxide).sub.1-11 (ATMER .RTM. 508)
C. Glycerol fatty acid ester (ATMER .RTM. 184)
______________________________________
EXAMPLE 1
In this Example, the copolymer added to the concentrate described above to
form the film was ionomer formed from a copolymer of ethylene with 15% by
weight of methacrylic acid (MI=14 g/10 minutes) an 22% neutralized by Zn
ion. The resultant film compositions consisted of 13.5 weight % of the
acid copolymer, 85 weight % of the ionomer and 1.5 weight % of the
antistatic compound identified in Table I.
Table I shows the time in Sec. for the 5000 volt d.c. charge imposed on the
film to dissipate to only 500 volts d.c. at various film ages from the
time of manufacture of the film. Samples of film were taken from the
conditioning/storage area for each test and then returned to this area for
further aging until the next test.
TABLE I
______________________________________
Film Composition
(d)
(a) (b) (c) 0.75%
1.5% 1.5% 1.5% Antistat A
Antistat A
Antistat B Antistat C
0.75%
Film Static.sup.1
Static Static Antistat B
Age Decay Decay Decay Static Decay
(Days) (Sec.) (Sec.) (Sec.) (Sec.)
______________________________________
7 8.77 --.sup.2 24.26 4.05
12 14.53 35.16 17.15 2.94
20 11.75 20.08 9.36 1.74
26 10.10 5.06 5.58 1.28
33 9.21 0.88 4.32 1.10
40 8.62 1.64 3.32 1.06
47 7.71 1.07 2.10 0.91
______________________________________
.sup.1 The film age for this composition was 8, 14, 21, 27, 34, 41, and 4
days, respectively.
.sup.2 The static decay for this film composition at this age, could not
be measured because the film could not be fully charged to 5000 v.d.c.,
indicating poor antistat capability.
Film (d) represents the present invention. This film shows a rapid decay
after only one week after film manufacture, and by about three weeks after
film manufacture, the electrostatic charge on the film decays within two
seconds.
By way of comparison, films (a) and (c) exhibited much longer decay time at
the one week interval (film (b) was even more deficient), and at about the
three week interval, the minimum decay time for these films was greater
than nine seconds, or more than 4.times. longer than for film (d) of the
present invention. The film aging times used for film (a) were in fact one
day longer than shown in Table I, indicating that antistat A by itself is
even a poorer antistat in ionomer than suggested by Table I, because the
decay values shown for film (a) in the Table were measured after giving
the film one day longer for static decay than shown in the Table.
As the films age, the time for static decay falls to a low level for all
the films (except film (a)). Film (d) has the advantage over films
(a)-(c), however, by much quicker static decay in the period up to about 4
weeks, so that the film can be used in packaging much sooner after
manufacture than films (a)-(c), with the result of substantially
diminished static electricity problem from such early use.
Table II shows additional film compositions for purposes of comparison to
the static decay results shown for film (d) of the present invention. The
film compositions are the same as for films (a) and (d), except for the
identity of the antistatic additive, which is shown in Table II.
TABLE II
______________________________________
Film Composition
(e) (f) (g)
0.75% A 0.75% B 0.50% A
Film 0.75% C 0.75% C 0.50% B
Age Static Decay
Static Decay
0.50% C
(Days) (Sec.) (Sec.) Static Decay (Sec.)
______________________________________
9 13.16 105.66 10.37
14 10.83 20.75 4.43
21 6.19 6.60 2.45
27 5.50 3.01 2.49
34 4.53 1.66 1.72
______________________________________
Films (f) and (g) were tested on a slightly delayed schedule as compared to
the schedule for film (d); film (e) was tested on about the same schedule
as film (d) (7, 12, 21, 26, and 34 days respectively). The delayed testing
schedule for films (f) and (g) gave them the opportunity to show improved
static decay (shorter decay times) and yet film (d) exhibits better
results.
From Table I and II it can be seen that combinations of antistat compounds
can give poorer results than obtained from the antistat compounds used by
themselves. Thus, the combination of compounds B and C in the film (film
(c)) give poorer results than when compounds B and C are used separately
(films (b) and (c), respectively). The combination of compound C with
compounds A and B (film (g)) gives a poorer result than when just
compounds A and B are combined (film (d)).
EXAMPLE 2
The procedure of Example 1 was followed to make and test the film
compositions described in Table III. The composition of films (h)-(j)
consisted of 18 weight % of the acid copolymer and 80 weight % of the
ionomer described hereinbefore and 2 weight % of the antistatic additive
identified in Table III.
TABLE III
______________________________________
(h) (i) (j)
2.0% 2.0% 1% Antistat A
Antistat A Antistat B 1% Antistat B
Film Static Film Static
Film Static
Age Decay Age Decay Age Decay
(Days) (Sec.) (Days) (Sec.)
(Days) (Sec.)
______________________________________
9 21.19 10 16.88 7 1.72
14 11.39 15 6.08 13 0.95
21 9.62 22 0.94 20 0.72
27 10.43 29 0.44 26 0.72
34 8.31 35 0.26 33 0.70
41 6.63 40 0.21 40 0.57
48 5.31 47 0.17 47 0.50
______________________________________
These results show the effects of higher levels of antistat compound(s) in
the film with film (j) of the present invention exhibiting superior
results for at least about the first two weeks after film manufacture.
EXAMPLE 3
The procedure of Example 1 was followed to make the film compositions
described in Table IV, using the same acid copolymer component described
hereinbefore and the ionomer was ethylene/(15 weight percent) methacrylic
acid copolymer neutralized 23% with Zn ion and having a M.I. of 5 g/10
minutes. The film consisted of 13.5 weight % of the acid copolymer, 85
weight % of the ionomer and 1.5 weight % of the antistat additive
identified in Table IV.
TABLE IV
______________________________________
Film Composition
(k) (l) (m)
1.5% 1.5% 0.75% A
Antistat A Antistat B 0.75% B
Film Static Film Static
Film Static
Age Decay Age Decay Age Decay
(Days) (Sec.) (Days) (Sec.)
(Days) (Sec.)
______________________________________
8 36.78 8 72.00 11 2.51
13 22.46 13 82.83 14 1.57
20 15.25 21 4.39 21 1.08
26 17.84 28 2.00 28 1.13
33 12.25 33 1.12 34 0.84
40 11.12 40 0.77 41 0.73
47 9.90 47 0.50 48 0.71
______________________________________
Film (m) is a film of the present invention and exhibited much faster decay
of static electricity for about the first four weeks after film
manufacture than either films (k) and (l) which used the antistatic
compounds by themselves.
When this Example was repeated, but using 1.5% of antistatic compound C by
itself, the time for stress decay over the period of 7 to 47 days from
64.13 to 2.36 Sec.
When this Example was repeated but increasing the level of antistatic
compound A by itself to 2.0% and antistatic compound B by itself to 2.0%,
the static decay ranged from 25.40 Sec. to 9.04 Sec. for film containing
compound A over the period of 7 to 47 days of film aging. For the film
containing antistatic compound B by itself, the static decay results were
as follows:
______________________________________
Film Age Static Decay
(Days) (Sec.)
______________________________________
7 62.41
14 10.73
21 2.74
28 1.25
33 0.65
41 0.42
______________________________________
By way of comparison, film of the present invention prepared by repetition
of this Example, but containing the combination of 1% antistatic compound
A and 1% antistatic compound B exhibited the following static decay
results:
______________________________________
Film Age Static Decay
(Days) (Sec.)
______________________________________
10 1.10
14 0.75
21 0.50
28 0.48
33 0.31
41 0.31
______________________________________
The combination of antistatic compounds in this film gave much better
static discharge performance for at least the first four weeks after film
manufacture as compared to the films described in the preceding paragraph.
As many widely different embodiments of this invention may be made without
departing from the spirit and scope thereof, it is to be understood that
this invention is not limited to the specific embodiments thereof except
as defined in the appended claims.
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